Curvature

Relative differences in composition, give relative differences in behavior. Ice, water and clouds are all made out of the same molecule (H2O). The relative size of the nuclei within the atoms is very tiny, when adding or subtracting a little heat, the atoms stay the same but the way they interact can cause major changes. In such a way that a snowball made of H2O can easily fly through mist made of H2O, while throwing a some mist will get you no where.

In an Aether composed of an air like matter (blue section), elastic collisions can be relatively straight forward. In a more dense setting (green section), particles can have curved trajectories.

There are 4 factors that influence curvature:

1. Density - friction with contact matter is needed, for curvature to happen.
2. Rotation - forward motion is generated, when spinning objects are in contact with other objects.
3. Frequency/Energy - In relation with forward motion 'spin' can have little or large consequences.
4. Structure - an object with a profile that has a different grip on it's surrounding matter will transfer its energy in a different manner.

The clips below illustrate these factors:

 

This last clip is a promotional clip for a Blitzball, wich has a special profile to generate more curve: